There seems to be a problem with some pansies and violas this year, with some of them succumbing to a rapid wilt and death
Not sure if the cause has been identified yet.
I had a couple turn up their toes within a few days of being purchased and planted out in a big tub - fortunately I had a few surplus to replace them with and now they all seem ok.
Don't think it's anything you've done wrong or could have changed - just one of those things this year. Hopefully they'll find out what's causing it soon.